This invention relates to a set comprising an intervertebral implant for immobilising a vertebra with respect to another and an instrument for installing this implant.
The invention also relates to a surgical method for immobilising a vertebra with respect to another.
It is well known to immobilise two vertebrae one with respect to another by means of an intervertebral implant in a rigid material, forming a cage defining a housing, this housing being designed to receive one or more bone grafts and/or cancellous bone chips. In some cases, the bone grafts and/or the cancellous bone chips can also be placed about the implant. The implant can restore a proper separation of the vertebrae and prevent a crash of a chip or more than one chip thereof. The immobilisation of the vertebrae with respect to the implant is achieved by the growth of bone cells on the one hand through the graft or grafts and/or chips, but also on each side of the implant, leading to what is termed a “merger” of the two vertebrae.
Some intervertebral implants have a reduced width, allowing their positioning through a posterior approach, on each side of the spinal cord. It is then generally necessary to position two implants, one on the left side of the spinal cord and the other on the right side.
This technique has the drawbacks of being relatively risky to implement, involving achieving a bone resection of the vertebra near the spinal cord, and forcing the use of reduced width implants, allowing only a small area of contact of the grafts with the vertebrae.
To overcome these drawbacks, it is possible to position an intervertebral implant by anterior approach. The approach being wider than the posterior approach, such an implant can have such a shape that it extends over a major portion of the surface of a vertebral plateau, and can therefore contain one or more grafts with a significant contact surface with the vertebral plateaus, which is a prerequisite for successful spinal fusion. An initiation through an anterior approach, however, has the disadvantage of revealing certain anatomical structures (in particular veins and arteries) that the orthopaedic surgeon or neurosurgeon is not accustomed to mobilise. This approach will therefore not be possible for a spine surgeon unless he is assisted by a colleague whose specialty is, for example, vascular surgery.
An alternative that allows solving temporarily the drawbacks of the two previous techniques consists in placing a single intervertebral implant positioned on the front side of the vertebra, occupying only a marginal surface of the intervertebral space and thereby freeing a significant surface area for the positioning of one or more grafts and/or bone chips. The implant is positioned by the posterior, side or intermediate approach between side and posterior, therefore slightly invasive. Document FR 2 923 158 describes an instrument for the introduction and implementation of such an implant, comprising a rod whose distal end is provided with means for mounting the implant, this instrument allowing (i) retaining the implant in the extension of the rod to achieve the introduction of the implant into the intervertebral space, with possible impaction, (ii) operating, once the introduction is achieved, a side pivoting of the implant with respect to the rod, in order to place the implant in the anterior position of the intervertebral space, and (iii) releasing the implant once the latter is in the position thereof of positioning in order to allow the removal of the instrument. Said mounting means comprise an articulated head equipped with a threaded rod and the implant comprises a threaded boring channel for screwing this implant on this articulated head.
Document WO 2008/019393 describes a similar instrument, connected to the implant by a double jaw, which in addition comprises a cable allowing to direct the implant with respect to the instrument.
The known instruments do not satisfy fully. In fact, the release of the implant can be difficult and achieve and lead to a change of the position of the implant during withdrawal of the instrument. The side pivoting of the implant with respect to the rod can be difficult to achieve or to control accurately, which can lead to a non optimal positioning of the implant in the intervertebral space. There is also a risk of longitudinal pivoting of the implant about itself during the operation of introducing this implant, leading to a faulty positioning of the implant; this faulty positioning is difficult to overcome once the implant is pivoted laterally or released.